Oil and gas wells produce oil, gas and/or byproducts from underground reservoirs. Oil and gas reservoirs are formations of rock containing oil and/or gas. The type and properties of the rock may vary by reservoir and also within reservoirs. For example, the porosity and permeability of a reservoir rock may vary from reservoir to reservoir and from well to well in a reservoir. The porosity is the percentage of core volume, or void space, within the reservoir rock that can contain fluids. The permeability is an estimate of the reservoir rock's ability to flow or transmit fluids.
Oil and gas production from a well may be stimulated by fracture, acid or other production enhancement treatment. In a fracture treatment, fluids are pumped downhole under high pressure to artificially fracture the reservoir rock in order to increase permeability and production. First, a pad, which is fracture fluids without proppants is pumped down the well until formation breakdown. Then, the fracturing fluid with proppants is pumped downhole to hold the fractures open after pumping stops. At the end of the fracture treatment, a clear fluid flush may be pumped down the well to clean the well of proppants.
An initial, or minifracture, test may be performed before a regular fracture stimulation treatment to calculate formation and fracture properties. Recently, analysis techniques were extended to the after-closure period. In this analysis, the after-closure data are analyzed to calculate formation permeability and reservoir pressure. This calculation hypothesizes the existence of either pseudo-radial or linear flow during the after-closure period.